La difícil cohabitación del Ejecutivo y el Congreso (2018-2020)

The risks assessed shall be evaluated based on the international risk acceptance criteria.

The ALARP principle has been adopted for risk evaluation. The ALARP region is that point at which the time, effort difficulty and cost of further risk reduction become out of proportion compared with the amount of risk reduction achieved.

Risks lower than the ALARP region risks will be considered minor risk and consequently they will not be considered.

Risks higher than the ALARP region risks will be considered major risk and consequently they will be not acceptable and further reduction measures are required.

The international risk acceptance criteria are presented in the following figure .

UNACCEPTABLE REGION

ACCEPTABLE REGION ACCEPTABLE REGION

(Risk must be demonstrated to have been reduced to a level which is practicable with a view to cost/benefit)

I N D I V I D U A L R I S K T O W O R K E R S

(including contractor employees)

I N D I V I D U A L R I S K T O T H E P U B L I C

(all those not directly involved with company activities)

A L A R P Benchmark existing installations

1 in 5,000 per year

ALARP Benchmark new installations

1 in 50,000 per year

A L A R P O R T O L E R A B I L I T Y R E G I O N 1 in 10,000 per year

Minimum tolerable limit 1 in 1 million per year Minimum tolerable limit

1 in 100,000 per year

Workers

Public

From the risk assessment and the international risk acceptance criteria the conclusion is presented in the following table.

No Calculated Risk Acceptable Risk Area Type Acceptance

1.0 4.5 E-05 1.0 E-05 Workers ALARP

2.0 9.0 E-05 1.0 E-05 Public ALARP

24 Risk Reduction Measures (Recommendations)

Risk reduction measures (Recommendations) may include reducing the risk by several technically feasible methods, generally are as follows:

• Measures to eliminate the risk.

• Measures to reduce the exposure of personnel to the hazards.

• Measures to reduce the frequency of occurrence.

• Measures to mitigate the consequences if the event does occur.

• Measures to improve evacuation in case of emergency (event occurs).

It has been concluded that the risk falls within the ALARP region for the individual risk to workers and public within the industrial area (PRS).

This is due to population density of the residential areas, as well as the population is present most of the time, while in the industrial areas the population is relatively low as well as because the existence of the safety precautions and procedures and the protection measures.

Since the calculated risk (ALARP region) is close to the acceptable region (1 X 10^-5), hence there are some minor risk reduction measures required to reduce the calculated risk beyond the acceptance border. These risk reduction measures (recommendations) are summarized as follows:

• It is strongly recommended to install an automatic fire detection system to activate ESD valve (or solenoid valve – depend on the PRS design) at the PRS station inlet in order to stop feeding the flame in case of fire

• The control room inlet door should be located in the upwind direction away from the PRS station (Inlet door should not face the PRS station).

• Alternatively, the control room should be provided by a secondary means of escape at the back side of the room, which shall be used in case of blockage of the main escape route by jet fires.

• Consider jet fire rated passive fire protection system be applied to all safety critical shutdown valves ESDVs or Solenoid valves in order to maintain small isolatable inventories. (As applicable)

• It is strongly recommended that the block isolation valve at the off-take point from the coming pipeline, to be placed in a safe place protected fro m jet fire for personnel intervention in case of emergency in order to isolate the pipeline as soon as possible.

• It is strongly recommended to have pipeline marking signs indicating in Arabic and in English

"Do Not Dig" and "High Pressure Pipeline Underneath" in order to prevent such extreme hazardous situation.

• It is recommended to include the prevailing wind direction on the PRS site plan.

• It is recommended to have an elevated wind sock installed in the PRS site, which can be seen from the control room and from outside the fence to determine the direction of gas migration in case of major gas leak.

• It is recommended to have a gas detection system within the PRS area to automatically sense the released gases as a percentage of LFL, in order to provide early warnings of gas release.

• Also, it is recommended to have point gas detectors at the control room HVAC intake to automatically sense the released gases as a percentage of LFL, in order to provide early warnings of gas release, if provided .

• Investigate a strategy to inform the residential area beside the PRS with the risk associated with the activities as well as the methods required for annunciating if any leak occurs.

• The design should fully comply with IGE TD/3 code requirements.

• There is a need to develop a safe system of work, based on risk assessment for dealing with potential gas leaks.

• Consideration should be given to the remote actuation of isolation and slam-shut valves by Town Gas SCADA System for PRS’s as well as the transmission and distribution pipelines.

• There is a need to produce Hazardous Area Classification drawings for all Pressure Reduction Stations.

• Review planned preventive maintenance policy and implementation.

• There is a need to produce a ‘Station Manual’ for each PRS. This manual should include formalized procedures, including precautions and a site scenario specific emergency plan.

• Site emergency plans must take into account wind direction and stability and should consider interfaces with other adjacent parties as well as the public living nearby.

• Town Gas needs to consider the security arrangements for all PRS’s.

• Consider formalizing procedures for filling the odorant storage tank, to include necessary precautions in the event of possible leaks.

• There is a need that Town Gas should apply risk assessment to all activities and to formalize procedures and permit-to-work systems.

25 Conclusion

Quantitative risk assessment study has been performed for the new facilities (Pressure Reduction Station and only the associated portion of the connecting pipeline) by Town Gas Company.

For the purpose of the analysis it has been assumed that the PRS open area is not normally manned but will be frequently visited by operations and maintenance teams comprising at least two personnel.

SHELL FRED version (4.0) has been selected for the consequence modeling of different types of hazardous consequences as follows:

• Flammable gas clouds

• Flash fires

• Jet fires

SHELL FRED version (4.0) is Shell’s suite of Fire, Release, Explosion and Dispersion models used to predict the consequences of the accidental or design release of product from process, storage or distribution operations.

For the PRS release scenario, the leak have been simulated based on 3 -hole sizes 0.25 inch, representing instrument fitting failure, 1.0 inch representing small pipe leak and 4.0 inches leak representing a 4-inch pipe full bore rupture or 4-inch hole size in a larger pipe diameter (corresponds to 5 -mm, 25-mm and 100 -mm), with wind speed of 1 m/s and stability class "F" representing "Very Stable" weather conditions and with wind speed of 10 m/s and stability class "A" representing " Very Unstable" weather conditions.

For the PRS gas dispersion scenario, the flammable gas dispersion distances (flash fires) have been simulated based on 3-hole sizes (5mm, 25mm and 100mm) and 2-wind cases (1F and 10A). The gas dispersion distances are calculated in terms of Lower Flammability Limits (LFL) and Upper

Flammability Limits (UFL).

The heat radiation from flash fires will not significantly affect equipment and structure due to the short duration of flash fires.

Flash fires are represented by the extent of the flammability limits of the released gases.

As a conclusion, flash fires are predicted to emanate from the PRS isolatable section. The pipeline flash fire presents the worst case scenario due to the relatively higher inventory and long duration of release potential.

The jet frustum fire (flame length) and heat radiation distances are measured in meters.

Process release failure frequencies and ignition probabilities have been identified for the detailed quantitative risk assessment (QRA) purposes.

Quantitative risk assessment (QRA) has been performed to all hazardous events developed from the scenario development section.

The risks have been assessed for the industrial workers and general public in different areas.

The risks assessed have been evaluated based on the international risk acceptance criteria.

It has been concluded that the risk falls within the ALARP region for the individual risk to workers and public within the industrial area (PRS).

Finally, risk reduction measures (recommendations) have been proposed to reduce the risk and improve the facilities safety standards.

26 References

1. NFPA 325M,

2. SHELL FRED Version (4.0) documentation,

3. Frank P. Lees, Loss Prevention in the Process Industries, 2001, 4. API-581, Risk Based Inspection recommended practice ,

5. IGE Codes, Institution of Gas Engineers and Managers, 6. Town Gas Project Documents.